Manganese

by Jack Norris, RD | Last updated: March 2013

Summary

There is a concern that manganese intakes in vegan diets can be high. To date, manganese toxicity in vegans has not been studied, but manganese toxicity usually does not occur with amounts of manganese found in the diet. However, iron deficiency can cause an increase in manganese absorption and vegans with iron deficiency should make sure they eat vitamin C at meals so that iron is absorbed instead of manganese.

Manganese in Vegan Diets

Manganese is a mineral that is essential for humans. It is part of the antioxidant system in the mitochondria, and is also involved in metabolism, bone development, and the creation of collagen for wound healing. Manganese is found in a wide range of plant foods.

Although manganese is an essential nutrient, manganese toxicity has been relatively common in places where workers are accidentally exposed to large amounts of manganese. Manganese in drinking water is the biggest concern since manganese in food is not as easily absorbed.

Manganese toxicity symptoms tend to be neurological problems. Headaches, muscle cramps, fatigue, and aggressiveness are early signs of manganese toxicity, which can then proceed into Parkinson's disease-like symptoms such as tremors (6). People with manganese toxicity have more of a tendency to fall backwards than do those with Parkinson's (6). Studies have been mixed on whether chelation therapy, the only therapy currently available, is successful at treating overt manganese toxicity (6).

According to the Linus Pauling Institute, "A single case of manganese toxicity was reported in a person who took large amounts of mineral supplements for years, while another case was reported as a result of a person taking a Chinese herbal supplement. Manganese toxicity resulting from foods alone has not been reported in humans, even though certain vegetarian diets could provide up to 20 mg/day of manganese."

The DRI for manganese if 1.8 mg for adult women and 2.3 mg for men. One study has measured the manganese intakes in vegans and it found an average intake of 4.1 mg for women and 5.6 mg for men (not including supplements) (1), though some vegans get much higher amounts. The upper tolerable limit for adults is 11 mg/day, although this level is considered "very conservative" by the Linus Pauling Institute.

Despite the fact that overt manganese toxicity from food rarely occurs, iron deficiency has been shown to increase the risk of manganese accumulation in the brain (6). Because iron and manganese share similar absorption mechanisms, iron deficiency can increase manganese intake (from the body trying to increase iron absorption but getting manganese instead) and high manganese intakes can depress iron absorption (3, 4). A study in miners whose drinking water was contaminated with manganese showed that manganese toxicity decreased iron status which returned to normal after the manganese was minimized in their environment (2).

People with liver damage are also at risk for manganese deficiency (6).

Manganese absorption is very low, from 1 to 5% (4). The phytic acid in a soy formula was shown to cut manganese absorption in half (from 1.6 to .7%) in adults (5). Phytic acid has a similar effect on iron absorption, but vitamin C can overcome phytic acid's effect on iron, whereas it does not do so for manganese (5).

From this research, it seems possible that long-term iron deficiency (not necessarily anemia, but low iron stores) could increase manganese absorption on a vegan diet high enough to cause problems, though I have not heard of any long term vegans getting Parkinson's-like symptoms or manganese toxicity.

Vegans with iron deficiency should make sure they eat vitamin C at meals so that iron is absorbed instead of manganese. Including some soy with meals for phytic acid might also be a good idea for such people.